Field of the Invention
The present invention relates to a microwave drying method of honeycomb formed body.
Description of the Related Art
Conventionally honeycomb structures made of ceramic have been used for a wide range of purposes, including a catalyst carrier to purify exhaust gas from automobiles, a filter to remove diesel particulates, and a heat storage member for combustion devices, for example. Such a honeycomb structure made of ceramic (hereinafter simply called a “honeycomb structure”) is manufactured by cutting a honeycomb formed body, which is prepared by extruding a forming material (kneaded material) prepared beforehand using an extrusion machine into a desired shape, into individual pieces of honeycomb formed bodies, followed by the steps of drying and end-face finishing, and then a firing step to fire at a high temperature.
Especially in recent years, the development of a honeycomb structure having low-pressure loss has been demanded for the purpose of improving the fuel consumption and making the purification performance more efficient. In order to lower pressure loss, the partition wall making up cells of the honeycomb structure has to be made thinner. In this respect, a honeycomb structure is loaded with a catalyst, and when the catalyst is loaded on the surface of the partition wall, then the partition wall including the catalyst layer will be thick substantially, and so pressure loss after loading with catalyst increases. In order to make the catalyst layer at the surface of a partition wall as thin as possible, the partition wall is required to have a higher porosity as well so as to allow more catalyst to be loaded in the pores of the partition wall. In order to manufacture a honeycomb structure including a thin wall of higher porosity, more pore former has to be added to the forming material. Since a water absorbable pore former is used to make the fluidity of the forming raw material favorable during extrusion, the honeycomb formed body will contain more water.
For a drying step to dry a honeycomb formed body, a microwave drying method is used, which is to irradiate the honeycomb formed body with microwaves. In this method, as drying progress, the water content becomes less and the drying efficiency deteriorates, and so hot air drying is used in combination as the final drying (see Patent Documents 1, 2).    [Patent Document 1] JP-A-2002-283329    [Patent Document 2] JP-A-2006-88685